tls: AES decrypt does one unnecessary memmove

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 11 insertions, 14 deletions

diff --git a/networking/tls.c b/networking/tls.c
index 55ad2d83f..fb49b1523 100644
--- a/networking/tls.c
+++ b/networking/tls.c
@@ -539,7 +539,7 @@ static void xwrite_encrypted(tls_state_t *tls, unsigned size, unsigned type)
         xhdr->type = type;
         xhdr->proto_maj = TLS_MAJ;
         xhdr->proto_min = TLS_MIN;
-        /* fake unencrypted record header len for MAC calculation */
+        /* fake unencrypted record len for MAC calculation */
         xhdr->len16_hi = size >> 8;
         xhdr->len16_lo = size & 0xff;
 
@@ -634,7 +634,7 @@ static void xwrite_encrypted(tls_state_t *tls, unsigned size, unsigned type)
         // AES_128_CBC   Block      16      16     16
         // AES_256_CBC   Block      32      16     16
 
-        /* Build IV+content+MAC+padding in outbuf */
+        /* Fill IV and padding in outbuf */
         tls_get_random(buf - AES_BLOCKSIZE, AES_BLOCKSIZE); /* IV */
         dbg("before crypt: 5 hdr + %u data + %u hash bytes\n", size, SHA256_OUTSIZE);
         // RFC is talking nonsense:
@@ -654,7 +654,7 @@ static void xwrite_encrypted(tls_state_t *tls, unsigned size, unsigned type)
         // It's ok to have more than minimum padding, but we do minimum.
         padding_length = (~size) & (AES_BLOCKSIZE - 1);
         do {
-                buf[size++] = padding_length;              /* padding */
+                buf[size++] = padding_length; /* padding */
         } while ((size & (AES_BLOCKSIZE - 1)) != 0);
 
         /* Encrypt content+MAC+padding in place */
@@ -796,26 +796,23 @@ static int tls_xread_record(tls_state_t *tls)
                 ) {
                         bb_error_msg_and_die("bad encrypted len:%u", sz);
                 }
-                /* Decrypt content+MAC+padding in place */
+                /* Decrypt content+MAC+padding, moving it over IV in the process */
                 psAesInit(&ctx, p, /* IV */
                         tls->server_write_key, sizeof(tls->server_write_key)
                 );
+                sz -= AES_BLOCKSIZE; /* we will overwrite IV now */
                 psAesDecrypt(&ctx,
                         p + AES_BLOCKSIZE, /* ciphertext */
-                        p + AES_BLOCKSIZE, /* plaintext */
-                        sz - AES_BLOCKSIZE
+                        p,                 /* plaintext */
+                        sz
                 );
                 padding_len = p[sz - 1];
-                dbg("encrypted size:%u type:0x%02x padding_length:0x%02x\n", sz, p[AES_BLOCKSIZE], padding_len);
+                dbg("encrypted size:%u type:0x%02x padding_length:0x%02x\n", sz, p[0], padding_len);
                 padding_len++;
-                sz -= AES_BLOCKSIZE + SHA256_OUTSIZE + padding_len;
+                sz -= SHA256_OUTSIZE + padding_len; /* drop MAC and padding */
                 if (sz < 0) {
                         bb_error_msg_and_die("bad padding size:%u", padding_len);
                 }
-                if (sz != 0) {
-                        /* Skip IV */
-                        memmove(tls->inbuf + RECHDR_LEN, tls->inbuf + RECHDR_LEN + AES_BLOCKSIZE, sz);
-                }
         } else {
                 /* if nonzero, then it's TLS_RSA_WITH_NULL_SHA256: drop MAC */
                 /* else: no encryption yet on input, subtract zero = NOP */
@@ -828,8 +825,8 @@ static int tls_xread_record(tls_state_t *tls)
         if (xhdr->type == RECORD_TYPE_ALERT && sz >= 2) {
                 uint8_t *p = tls->inbuf + RECHDR_LEN;
                 dbg("ALERT size:%d level:%d description:%d\n", sz, p[0], p[1]);
-                if (p[0] == 1) { /*warning */
-                        if (p[1] == 0) { /* warning, close_notify: EOF */
+                if (p[0] == 1) { /* warning */
+                        if (p[1] == 0) { /* "close_notify" warning: it's EOF */
                                 dbg("EOF (TLS encoded) from peer\n");
                                 sz = 0;
                                 goto end;